Mine tailings and mine reclamation efforts have evoked enormous environmental concerns in the United States and abroad. Tailings are waste products remaining in containment areas or discharged to receiving waters after metals are extracted from a particular site, and consist primarily of waste rock containing a variety of rock forming minerals, including as major constituent groups crystalline silica, feldspars and clay minerals; with minor constituent groups including carbonates, sulfates, sulfides and micas. Pollution issues associated with mine tailings relate to the structural integrity and stability of tailings containment areas and the potential for pollution impacts should containment failure occur. At the heart of these concerns is the pollution potential of mine tailings on ground and surface water, and correspondingly how such potential pollution affects people living in the immediate vicinity of tailings containment areas.
The need for effective mine reclamation strategies, and safe disposition of potentially hazardous mine tailings, is widely recognized in the mining and environmental industries alike. There is no legitimate doubt that disposing of mine tailings in a safe manner, as opposed to continually attempting their containment, is desirable from both an environmental safety and economic point of view. Likewise, other mineral waste materials raise similar environmental contamination concerns, and the need for their safe and effective disposition is also well acknowledged.
As far back as ancient Mesopotamia, researchers have located what they believe to be basalt rock slabs formed from silt. It is believed that inhabitants used the basalt rock as a main staple in the region for a variety of purposes, including pottery, architecture, writing materials, art objects and tools. In simulation studies to recreate the basalt rock from silt, researchers were able to approximate the composition and texture of the basalt rock using local alluvial silt as raw starting material, and heating the material within a defined temperature range over a sustained time period. The resulting basalt rock was characterized by matted clinopyroxene crystals embedded in a glassy matrix, with starting material remnants either rarely appearing in, or completely absent from, the final basalt rock. The basalt rock was most likely of limited strength, as it lacked an aggregate microstructure. Due to the observed presence of many large pores, some as big as 3 mm, the basalt had high water absorption, likely well in excess of 7%.
In more recent examples of waste materials, fly ash and bottom ash from burning coal for electric power are largely incombustible residuals formed from inorganic minerals in coal. Roughly hundreds of million tons is produced every year in the USA alone. Fly ash and bottom ash are also produced in waste incinerators and biomass-fueled power plants. Slag mineral waste materials result from metal processing operations. Quarry and dredging operations often produce silicate waste materials such as fines or slimes that must be disposed of in a safe manner.
Relatively pure mineral materials (kaolinite clay, feldspar, quartz, talc, etc.) have conventionally been used to manufacture a variety of ceramic materials with varying compositions and degrees of quality. As previously described, non-vitreous Dal-Tile, semi-vitreous Balmor Tile and vitreous Granitifiandre Kashmir White tile represent a very few. However, these and a vast array of other conventional ceramic products (ceramic tile, dinnerware, sanitaryware, etc.) are typically manufactured by methods that rely on the plasticity and bonding (in the unfired state) of clay—largely kaolinite—and generally use relatively pure raw materials. As previously stated, conventional ceramics also demonstrate a number of undesirable characteristics, including moderate to high porosity and water absorption, low hardness and strength, and the absence of secondary crystallite formation upon cooling, which contributes to product durability. Also, in the manufacture of conventional ceramics, considerable concern is placed on the quality and purity of the raw material ingredients. Further, contaminants in the raw materials can cause considerable damage to the quality of the conventional product in terms of structural integrity and defects in the cosmetic properties. Surprisingly, Applicant's process and composition are tolerant of higher concentrations of many materials that are considered contamination in conventional ceramics manufacture. Such materials include iron, magnesium, manganese, sulfur, and their compounds.
The need exists in the environmental clean-up industry to develop an effective and efficient strategy for reclaiming mines, disposing of mine tailings after mineral extraction at the mine is complete, disposing of mine development rock, disposing of fly ash and bottom ash from power plants or incinerators, disposing of slag, and disposing of fines or slimes. An equally significant need exists in the synthetic rock industry to produce a low porosity, easily manufactured, low absorption vitreous tile in a cost effective and relatively fast manner.